1. Field of the Invention
The present invention relates to a thermal printer, and, more particularly, to a thermal printer which can print a high-quality image by properly dissipating heat generated by a line thermal head.
2. Description of the Related Art
Referring to FIG. 3, a related thermal printer 31 has a platen roller 32 and a line thermal head 33 disposed in a frame 31a. The line thermal head 33 is situated above the platen roller 32. A recording sheet 34 is transported between the line thermal head 33 and the platen roller 32.
The line thermal head 33 is mounted to a long head mount 35. Respective ends of a pair of head levers 36 are mounted to both ends of the head mount 35 in a longitudinal direction thereof.
The illustrated right end of each head lever 36 is supported by a rotary shaft 37 fixed to a side plate of the frame 31a, so that an end of each head lever 36 to which the line thermal head 33 is mounted is rotatable around the rotary shaft 37 serving as a fulcrum.
An ink ribbon 39 accommodated in a ribbon cassette 38 is routed between the platen roller 32 and the line thermal head 33.
A sheet-feed roller 40 and a press-contact roller 41 are disposed on the left of the platen roller 32. A recording sheet 34 press-contacted and nipped between the sheet-feed roller 40 and the press-contact roller 41 can be transported in the direction of arrow A (corresponding to the direction of transportation of the recording sheet 34 when printing is to be performed) or in the direction of arrow B opposite to the direction of arrow A.
A ribbon separating member 43 is, through a heat insulator 42, disposed downstream from the head mount 35 in the direction of transportation of the recording sheet 34.
A printing operation of the related thermal printer 31 will be described.
With the line thermal head 33 being separated from the platen roller 32 in a head-up state as a result of clockwise rotation of the head levers 36, the ribbon cassette 38 is mounted in the frame 31a. This causes the ink ribbon 39 to be routed between the platen roller 32 and the line thermal head 33.
Next, a recording sheet is fed in the direction of arrow B by a sheet-feed mechanism (not shown) and is nipped between the sheet-feed roller 40 and the press-contact roller 41. From this state, the recording sheet 34 is further transported in the direction of arrow B by the sheet-feed roller 40 and the press-contact roller 41 to a location between the line thermal head 33 and the platen roller 32.
When a starting position of the recording sheet 34 is located by transporting an edge 34a of the recording sheet 34 up to the vicinity of the sheet-feed roller 40, the line thermal head 33 press-contacts the platen roller 32 with the ink ribbon 39 and the recording sheet 34 in between so as to be in a head-down state.
Selectively heating a plurality of heater elements of the line thermal head 33 while transporting the recording sheet 34 in the direction of arrow A with the line thermal head 33 in the head-down state causes ink of the ink ribbon 39 to be thermally transferred to the recording sheet 34, so that a predetermined image is printed on the recording sheet 34.
Here, the ink ribbon 39 which has been made hot for performing the printing is cooled by the time it reaches the ribbon separating member 43 with which the ink ribbon 39 comes into sliding contact, and is properly separated when it is cooled. The heat insulator 42 disposed between the line thermal head 33 and the ribbon separating member 43 can prevent the heat of the line thermal head 33 from being transmitted to the ribbon separating member 43. Refer to Japanese Unexamined Patent Application Publication No. 2002-144616.
Although, in the related thermal printer 31, the heat that is generated by the line thermal head 33 when printing is performed is transmitted to the head mount 35 and is dissipated, the heat cannot be dissipated quickly enough from the head mount 35 when high-speed printing is carried out, causing the temperature of the line thermal head 33 to be equal to or greater than a predetermined value. Therefore, unnecessary ink is transferred from the ink ribbon 39, causing, for example, a thread-forming phenomenon to occur, that is, streaks to be produced in an image printed on the recording sheet 34. This may reduce print quality.